There's some useful hobby skills here for terrain builders. Numerous successive coats of adhesive tile grout mixed with acrylic paints has given a rock hard finish. I went over it a black wash and then I've dune successive lighter drybrushes to bring out the textures my brother carved into the foam.
Also I put in the 'sky' and most of the 'clouds' are there to hide where the paint was too thin!
Unfortunately he's had a bit of a setback since these pictures. The matt floor varnish recommended to protect the paintwork and surface has had a reaction, the result is not unlike the frosting problem I've had with Purity Seal. He followed the directions to thin the varnish down and it's painted on, not sprayed and the end result looks like the sugar coating you get on Frosties!
We're not sure how to fix this, I don't know whether its, start from scratch or just cover the areas of frosting, although they're widespread and it'll be a nightmare to blend that back in. It's a big problem and I feel his pain. Hopefully the forums he goes on may have experienced this same problem and have a solution.